The Prince of Wales has asked a leading independent economist to examine whether the use of complementary therapies could save the NHS money, Clarence House said yesterday.

Christopher Smallwood, a former chief economics advisor to Barclays bank, is carrying out the report on behalf of Prince Charles to "look at the effectiveness, especially from a financial point of view, of integrated healthcare".

Paddy Haverson, the prince's spokesman, said the report was still at the first draft stage and it was hoped it would be completed by October.

A leaked draft of the report's conclusions said "economy-wide" savings of between £500m and £3.5bn could be achieved by offering spinal manipulation therapies, such as chiropractic therapy, as a standard NHS option for back pain, according to the Times.

The report also claims up to £480m could be cut from the prescription drugs bill if 10% of GPs offered homeopathy as an alternative to standard drugs, according to the paper.

In addition, £38m could be saved by switching 10% of depression patients to St John's Wort, a herbal remedy.

Mr Haverson said the prince had not sought to influence the outcome of the study and that was why he had asked an independent economic expert to examine the costs.

Mr Smallwood is not involved with the Prince of Wales's Foundation for Integrated Health (FIH), which Charles founded partly to establish a place for alternative and complementary therapies in the NHS.

But he would not comment on the contents of the report. "It is entirely inappropriate for anyone to be commenting on the report when it has not even been completed, let alone published," he said.

"The Prince of Wales merely asked an eminent independent economist to look at the effectiveness, especially from a financial point of view, of integrated healthcare."

Clarence House also denied claims in the Times that the prince was breaching his constitutional role in publishing the report and said it "refuted suggestions about influencing government policy", arguing that the report would be made public and not specifically sent to any ministers.

This year the FIH issued its first guide for patients on how to seek complementary treatments from the state service, private practitioners or charities.

Nearly 6 million people - almost one in 10 members of the population - opt for complementary care each year, and a host of people in the public eye, from Madonna to Cherie Blair, are interested in an approach that may have once been called "way out".